Wireless communication devices such as User Equipment (UE) are also known as e.g. wireless terminals, mobile terminals and/or mobile stations. UEs are enabled to communicate or operate wirelessly in a wireless communication environment comprising multiple mobile communications networks, such as cellular communications networks which comprising Second/Third Generation (2G/3G) networks, 3G Long Term Evolution (LTE) networks etc. In these communications networks, a cell search procedure is usually performed in the UE, which consists of a series of synchronization stages by which the UE determines time and frequency parameters that are necessary to demodulate downlink (DL) signals received from a network node and to transmit uplink (UL) signals to the network node with the correct timing.
For example, in the 3GPP specifications for LTE, a DL signal transmission is mandatory, e.g., a synchronization signal, with fixed and known timing or periodicity or frequency position, in order to enable an initial UE access. Specifically, to assist the UE to perform a cell search, two special signals are transmitted on each downlink component carrier: the Primary Synchronization Signal (PSS) and the Secondary Synchronization Signal (SSS). The time synchronization in 3G LTE network is performed by the UE in two stages. The first stage is a coarse time synchronization, to acquire a symbol timing by detection of the synchronization signal PSS. The coarse time synchronization obtained from the synchronization signal is rather rough and with large timing error. The second stage is fine time synchronization, which is obtained based on Common Reference Signal (CRS). Since CRS occupies much wider bandwidth than the synchronization signal does, it offers much higher timing resolution.
The next generation of mobile communications networks, e.g. 5G networks, is currently emerging, where massive beamforming may be employed as a useful component. One envisioned solution is that each network node has a large number of narrow fixed beams that a UE can be connected to, so called grid-of-beams beamforming. Consequently, one aspect of the design is to minimize the static always-on signals or beams in order to reduce energy consumption at the network node side and to reduce interference to UEs served by the neighbouring base stations or network nodes. Thus CRS may not be employed anymore in 5G networks. Data demodulation relies on DeModulation Reference Signal (DMRS), which only exists in transmit time intervals (TTIs), i.e. scheduled time intervals that are allocated for a UE specific transmission, when there is data to be transmitted to the UE on Physical Downlink Shared Channel (PDSCH), and only in resource blocks (RBs) where PDSCH is allocated.
Therefore, the state-of-art solution for time synchronization in 3G LTE network cannot be used for the next generation of mobile communications networks. Further, it is not possible to achieve high timing accuracy and low computational complexity at the same time in the state-of-art solution.